Answer:
The sentence above is a complex sentence.
Explanation:
A complex sentence has one independent clause and at least one dependent clause. An independent clause can stand alone as a sentence as it represents a complete thought. In the sentence above, the dependent clause is the following prepositional phrase: "after some time passed". Then the independent clause is the following sentence: "baseball's second league was created". As you can see, 1 cannot stand on its own because it does not represent a complete idea.
1) *After some time passed
2) Baseball's second league was created
